Mouse not disappearing on fullscreen YouTube!?

I am really enjoying using Vivaldi as of yet but there has been one major problem for me. I use YouTube quite a bit, however, the mouse will not disappear while watching the video. Sites with the same sort of player also have this issue. If I could get any help that would be great. (I am using the latest snapshot 1.1.453.6, but has occurred on every other version)